Reciprocal ferrite film phase shifter having latching conductor film

ABSTRACT

THE PHASE SHIFTER COMPRISES AN INTEGERAL STRUCTURE OF FIRST AND SECOND SEPARATELY DEPOSITED FERRITE LAYERS AND AN INTERMEDIATE CONDUCTING FILM DEFINING ORTHOGONAL LATCHING CURRENT CONDUCTING PATHS AND SERVING TO STRUCTURE THE FERRITE FILM IN A DOUBLE TORROID CONFIGURATION. A MICROWAVE TRANSMISSION LINE INCLUDES A MICROSTRIP DEPOSITED ON THE SECOND FERRITE LAYER DEFINING THE DIRECTION OF PROPAGATION OF MICROWAVE ENERGY. ENERGIZATION OF THE CONDUCTING FILM FOR ESTABLISHING A FLOW OF LATCHING CURRENT IN A SELECTED ONE OF THE CONDUCTING PATHS THEREIN PROVIDES FOR FLUX DRIVING THE FILM TO A REMANENT CONDITION OF MAGNETIZATION IN A CORRESPONDING, DESIRED ORIENTATION, PARALLEL OR PERPENDICULAR TO THE DIRECTION OF MICROWAVE PROPAGATION. WHERE B IS THE PROPAGATION CONSTANT OF THE MICROSTRIP, RELATIVE   DIFFERENTIAL PHASE SHIFT IS EXPRESSED AS $B/B, AND IS A FUNCTION OF THE REMEANENT FIELD STRENGTH IN THE DIRECTION OF PROPAGATION. ALTERNATE CURRENT PULSING OF THE CONDUCTING FILM TO ESTABLISH LATCHING CURRENT IN ALTERNATE ONES OF THE CURRENT PATHS PERMITS RAPID SWITCHING BETWEEN MINIMUM AND MAXIMUM RELATIVE PHASE SHIFT CONDITIONS.

D. c. BUCK 3,566,311 RECIPROGAL FERRITE FILM PHASE SHIFTER HAVING Feb.23, 1971 Fiied May 2,1969

LATCHINGCONDUCTOR FILM 1 2 Sheets-Sheet 1 mvmmn DANIELC. BUCK J5 w FIG,5

f BY W ATTURNEY Feb. 23, "1971 D. c. BUCK 3,566,311

REC'IPROCAL FERRITE. FILM PHASE SHIFTER' HAVING LATGHING CONDUCTOR FILMFiled May 2, 1969 2 Sheets-Sheet z ATTORNEY United States Patent U.S.Cl. 333-31 9 Claims ABSTRACT OF THE DISCLOSURE The phase shiftercomprises an integral structure of first and second separately depositedferrite layers and an intermediate conducting film defining orthogonallatching current conducting paths and serving to structure the ferritefilm in a double torroid configuration. A microwave transmission lineincludes a microstrip deposited on the second ferrite layer defining thedirection of propagation of microwave energy. Energization of theconducting film for establishing a flow of latching current in aselected one of the conducting paths therein provides for flux drivingthe film to a remanent condition of magnetization in a corresponding,desired orientation, parallel or perpendicular to the direction ofmicrowave propagation. Where is the propagation constant of themicrostrip, relative differential phase shift is expressed as Afl/fi,and is a function of the remanent field strength in the direction ofpropagation. Alternate current pulsing of the conducting film toestablish latching current in alternate ones of the current pathspermits rapid switching between minimum and maximum relative phase shiftconditions.

BACKGROUND 'OF THE INVENTION Field of the invention This inventionrelates to a reciprocal ferrite film latching phase shifter formicrowave transmission in the T.E.M. mode, and more particularly, tosuch a phase shifter of improved, integral construction employing aconducting film defining the latching current paths for flux driving ofthe ferrite film.

Description of the prior art Heretofore in the prior art, substantialstudy and investigation has been made of the effects of propagation ofmicrowave energy, particularly in ferrite-loaded micro- Wavetransmission circuits. Ferrite loading of such circuits provides forselective control of the amount of relative, or differential phase shiftof the microwave energy propagated through the circuits. The amount ofphase shift is a function of the frequency of the microwave energy, thecircuit configuration, the characteristics of the ferrite, and thestrength of the component of the DO magnetizing field in the directionof propagation of microwave energy through the microwave transmissioncircuit.

Generally, the component of magnetization in the direction ofpropagation of the microwave energy through a ferrite-loaded microwavetransmission circuit controls the effective permeability of the ferriteto that microwaveenergy propagation. This control of the effectivepermeability in turn controls the phase velocity of the microwave signalpropagated through the circuit. By varying the effective permeability inthe direction of propagation, varying amounts of differential phaseshift of the microwave signal may be realized.

The applied magnetizing field for the ferrite loading element may beestablished either by continuous supply of a magnetizing current tosuitable conductor means, such as a solenoid, associated with theferrite element or by a latching magnetizing current which controls theferrite element to a remanent state of magnetization. Generally, thelatching type operation is preferred since it requires less power, andthe amplitude control of the magnetizing current is not as critical.Also, the latching operation is more readily adapted for digitalcontrol.

Reciprocal phase shift in a ferrite-loaded microwave transmissioncircuit requires that the applied D.C. magnetization be parallel to thedirection of propagation of the microwave energy. By contrast,nonreciprocal phase shift results from the condition that the appliedD.C. magnetization is perpendicular to the R.F. (radio frequency)magnetic field associated with the microwave propagation, and whichfield is elliptically polarized. This latter condition produces thenonreciprocal effect of different amounts of phase shifts for differentdirections of wave propagation.

As is well known, a wave guide transmission circuit cannot support aT.E.M. mode of transmission. Therefore, the condition for reciprocalphase shift cannot be realized in a ferrite-loaded wave guide. Bycontrast, a microstrip circuit may support a T.E.M. mode, and thus thecondition for reciprocal phase shift may be realized in a ferriteloadedmicrostrip circuit.

Heretofore, reciprocal latching, or remanent, ferrite phase shiftersoperable with T.E.M. microwave transmission systems have been veryunsatisfactory in their design and effectiveness. As noted, reciprocalphase shift is achieved by applied D.C. magnetization in the directionof propagation. In general, however, a latching current cannot bedeveloped in the direction of propagation in one of the conductors of aT.E.M. transmission system to achieve latching, because a currentdirected in the direction of propagation of the wave energy cannotproduce a magnetic field having a component in that direction. As aresult, the latching circuit configurations developed heretofore havebeen of complex design to assure avoidance of interference of thelatching current and resultant applied D.C. magnetizing field with themicrowave propagation.

One design of the prior art is the so-called coplanar type of reciprocalferrite T.E.M. latching phase shifter. In this structure, the appliedmagnetization field is coplanar with the microwave transmission line.There results a poor distribution of the applied magnetizing field aboutthe microwave transmission line or strip, and in neither state oflatching for minimum or maximum relative phase shift are the fields ofapplied magnetization exactly parallel or perpendicular to the directionof propagation of microwave energy.

Other phase shifters of the subject type proposed heretofore haverequired stringent and impractical control of the dimensions andconfigurations of component portions of the phase shifter structures andparticularly of the ferrite which sustains the remanent D.C. magnetizingfield. Such devices are not only unfeasible for commercial productionbut also introduce undesirable and unacceptable operating parameters,such as prohibitively high insertion losses.

SUMMARY OF THE INVENTION- The foregoing and other defects of prior artreciprocal ferrite film latching phase shifters, for use with microwavetransmission systems in the T.E.M. mode, are overcome by the phaseshifter of the invention.

The present invention comprises an improvement of the inventiondisclosed and claimed in the copending application Ser. No. 821,344entitled, Reciprocal Ferrite Film Latching Phase Shifter, of Daniel C.Buck and Leonard Dubrowsky, filed concurrently herewith. In thatinvention, the latching current is supplied by pulsing of conductorsreceived in channels provided therefor in the ferrite film. Theformation of such channels is a difficult task, where a single ferritefilm is to be employed. Due to the small dimensions of the film,sophisticated techniques such as ultrasonic drilling must be used toform the channels through which the conductors must then be inserted. Analternative construction technique requires use of two separate ferritelayers at the common interface of which suitable channels are definedand which then are assembled, preferably with the latching conductors inplace. Such an assembly requires accurate finishing of the juxtaposedsurfaces of the two ferrite film portions to assure completion of a lowreluctance magnetic path across the interface.

'In accordance with the invention, the phase shifter comprises acontrolled flux driven, ferrite film having a latching conductorstructure formed integrally therewith, and an associated, microwavetransmission line. More particularly, the ferrite film is formed insuccessive steps in lower and upper layers, or portions, and aconducting film defining latching current paths for flux driving of thefilm is found in an intermediate step between the lower and upperferrite layers. The portions of the ferrite layers surrounding theconducting film comprise an integral structure, providing an excellentmagnetic circuit or path. The successive layers of the ferrite film andthe conducting film may be produced "by chemical deposition techniques.The lower layer or portion, of ferrite material is deposited, preferablyon a suitable supporting substrate, and next a conducting film ofplatinum or refractory material is deposited. The conducting film isthen formed, as by conventional photoresist processes, to define thedesired orthogonal latching current conducting paths, each of which iscentrally located with respect to corresponding edges of the ferritefilm. The second layer, or portion, of the ferrite film is thendeposited. The conducting film structures the ferrite film to defineeffectively a double toroid which may be selectively driven to states ofremanent magnetization by selectively supplying latching currents toappropriate ones of the conducting paths of the latching film. Amicrowave transmission line, or microstrip, is formed on the ferritefilm, preferably by a deposition and conventional photoresist process,with the microstrip centrally located on the film. Preferably, theorthogonal latching conductor paths defined by the conducting film areoriented with respect to the microstrip to establish applied magnetizingfields oriented, respectively, parallel and perpendicular to thedirection of propagation of microwave energy through the microstrip.

The microwave transmission line includes the microstrip deposited on theupper surface of the ferrite and a common ground plane parallel to theplane of the microstrip and spaced therefrom by a dielectric layer. Inone embodiment, a dielectric layer and a ground plane are formed insuccessive steps on the microstrip and upper surface of the ferritefilm. In another embodiment, the conducting film serves a dual functionas the ground plane for the transmission line and the dielectric isprovided by the upper layer, or portion, of the ferrite film.

In operation, microwave energy propagated through the microwavetransmission line establishes an electrostatic field between themicrostrip and its ground plane. By pulsing the conducting film toestablish current flow in selected ones of the orthogonal latchingcurrent paths, there are produced corresponding and orthogonally relatedapplied D.C. magnetizing fields for latching the film in correspondingremanent magnetized conditions of the same orientation as the appliedfields. The latching currents thus provide a selectively controlled fluxdrive of the ferrite film to desired orientations of remanentmagnetization.

The RF. magnetic field resultant from the microwave propagation throughthe transmission line exists within the ferrite. The remanent D.C. fieldof the ferrite, produced by current pulsing through a selected latchingcurrent conductor path interacts with the RF. magnetic field 4 of themicrowave to produce a resultant differential phase shift.

Where ,8 is the propagation constant of the microstrip, the relativephase shift can be expressed as Aft/[3 and is a function of thecomponent of the applied D.C. magnetization field in the direction ofpropagation. The phase shift 5, as is well known, is a function of thefrequency of the microwave transmission, and of the circuitconfiguration and characteristics of the ferrite, including its lengthin the direction of propagation. Thus, as the component of DC.magnetization in the direction of propagation is alternated betweenmaximum and minimum values by pulsing of the appropriate latchingconductors, the relative phase shift is likewise varied between maximumand minimum amounts. The relative phase shift effect is reciprocal anddoes not depend on the direction of the DC. magnetizing field but onlyits angle or orientation with respect to the direction of microwavepropagation.

The reciprocal phase shift characteristic permits for compact design ofthe phase shifter by forming the microstrip into a spatially periodiccircuit such as a meander line. The meander line is centrally positionedon the ferrite film, and provides maximum interaction of the RE. and DC.magnetization fields. However, at high frequencies such as X band, theguide wave length is so short that for applied magnetizing fields ofreasonably high amplitude, the meandering is not required.

T he phase shifter of the invention utilizes the desirablecharacteristics of latching, or remanent, magnetization and thereciprocal phase shifting effect to achieve a structure compact in sizeyet highly effective in producing rapidly and easily controlled phaseshifting of microwave transmission in the T.E.M. mode. The structure asdescribed provides for maximizing the orientation of the applied D.C.magnetization fields in either exactly parallel or exactly perpendicularorientations with respect to the direction of propagation of themicrowave energy. In particular, the integral structure afforded byvirtue of the deposited conducting film affords a more uniformdistribution of the latching currents and the DC. magnetizing fieldsproduced thereby, and thus a more uniform region for interaction of theresultant fields of remanent magnetization of the ferrite and the RF.magnetic fields generated by the propagated microwave. Thus, in additionto providing a simplified structure of compact size, the phase shifterof the invention is very efficient in operation and provides for highlyaccurate, and quickly and easily controlled phase shifting of microwavesignals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aphase shifter in accordance with the invention;

FIG. 2 is a planar view of the latching current conducting film employedin the phase shifter of the invention;

FIG. 3 is a planar, schematic view of the phase shifter of FIG. 1 withcertain portions thereof broken away to facilitate an explanation of thetheory of operation of the phase shifter;

FIG. 4 is a cross-sectional view of the phase shifter of FIG. 1, takenalong the line 44 in FIG. 3;

FIG. 5 is a plot of a hysteresis curve defining the magnetizationcharacteristics of the ferrite film employed in the phase shifter of theinvention;

FIG. 6 is a planar, schematic view of a phase shifter in accordance witha second embodiment of the invention; and

FIG. 7 is a cross-sectional view of the phase shifter of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION The phase shifter of the inventionis of very compact size and relatively simple in design, yet providesfor highly accurate and rapid control of relative, or differential,

phase shift of microwave energy propagated through a microwavetransmission line, or microstrip, associated therewith. Further, thephase shifter provides for rapid switching between selected phase shiftconditions, as described more fully hereinafter. To facilitate anunderstanding of the phase shifter of the invention, it has been shownin the drawings on a greatly enlarged scale, particularly in thethickness or height dimension.

In FIG. 1, the phase shifter includes a ferrite film 12 of anyferrimagnetic material, and which may be formed on a support (notshown). A microwave transmission line, or microstrip 14 is deposited onthe ferrite film 12. As shown, the microstrip 14 is formed as a meanderline, including a number of convolutions having long, parallel legs 14a,and short, parallel legs 14b at right angles to the legs 14a. The legs14a define the primary direction of propagation of microwave energythrough the microstrip line 14. The spacing of the legs 14a preferablyis approximately one-eighth the wave guide length.

A dielectric layer 16 is deposited on the surface of the film 12 andover the meander line 14. A ground plane 18 is formed on the dielectriclayer 16. The microstrip circuit 14, the dielectric 16, and the groundplane 18 together provide the microwave transmission circuit of thephase shifter 10. Suitable coaxial connectors 20 and 22 are mounted onthe phase shifter 10 with a common ground connection to the ground plane18 and having coaxial connector elements 21 and 23, respectively,connected to opposite ends of the meander line 14.

Each of the ferrite film 12, the line 14, the dielectric layer 16, andthe ground plane 18 may be formed by suitable chemical depositiontechniques.

The thicknesses of the component portions of the structure are greatlyenlarged in scale, and in practical circuit of the ferrite anddielectric layers 12 and 16 are of 25 to 50 mils in thickness, and theground plane 18 may be of substantially less thickness. The meander line14 may be less than 1 mil in thickness and to mils wide. For a lateraloverall dimension of about two inches square for the phase shifter 10,the meander line 14 occupies a central area of about 1 /2 inches square,including a total length of about five inches. The dimensions are notcritical, however, and may be varied as required. The only criticallimit is that the ferrite film be of sulficient thickness to avoidFaraday rotation effects.

As previously described, a conducting film is formedintermediate upperand lower portions of the ferrite film 12 to provide, or define,latching current conductor paths which are selectively energized forestablishing desired orientations of the remanent magnetization of theferrite film 12. In FIG. 1, the conducting film is shown by hidden linesand identified by the numeral 25. The film may be planar, and ofsubstantially square or rectangular configuration as shown of somewhatsimilar dimensions than the external dimensions of the ferrite film 12.Further, the film 25 is provided with pairs of tabs 26 and 27 whichdefine the direction of current paths therethrough.

In FIG. 2 is shown the film 25 in a planar view with the other portionsof the phase shifter 10 removed. If desired, an opening 24 may beprovided in the interior of the film 25 to assure spreading of thecurrent paths through the film and between corresponding pairs of thetabs. AS illustrated, the opening 24 assures that the current pathsindicated by dotted lines 26 substantially spread throughout thedimension of the film 25, between the associated tabs 27. A similarspreading of the current path between the tabs 26 would occur.

Referring again to FIG. 1, the film 25 is formed as an intermediate stepin the formation of the film 12. Particularly, following deposition of afirst portion or layer of the film 12, the conducting film 25 isdeposited and suitably formed, as by conventional etching processes, tothe configuration as best seen in FIG. 2. The film preferably is ofplatinum or a refractory metal. The conducting film 25 need not be morethan a few mils in thickness. If desired,

prior to or simultaneously with the completion of the deposition of thefilm 12, connectors as schematically illustrated at 28 and 29 may beafiixed to the tabs 26 and 27 of the film 25 to provide for electricalconnection to the film. Preferably, the second layer of the ferrite film12 above the conducting film 25 is of less thickness than the portionbelow the conducting film 12.

In FIG. 3 is shown a simplified and somewhat schematic, planar view ofthe phase shifter of FIG. 1 and in FIG. 4 is shown a cross section ofthe phase shifter, taken along the line 44 in FIG. 3. In FIG. 5 is showna hysteresis curve of a ferrimagnetic material such as the film 12.Reference will be had concurrently to FIGS. 3 through 5 in discussingthe operation of the phase shifter of the invention.

In FIG. 3, the latching film 25 is shown by hidden lines to indicate itscentral location with respect to the major dimensions, or edges of thefilm 12 in the completed structure and also to illustrate thestructuring of the ferrite film 12 resultant from the provision of thefilm 25 therein. Particularly, interconnected portions of the ferritefilm 12 adjacent each edge thereof provide for a completed magnetic pathpast the boundary of the edges of the film 12 and between the adjacentedges of alternate tabs 26 and 27. These regions effectively define adouble toroid construction of the ferrite film 12. The dual toroid construction of the ferrite film, as defined by the conductor film 25, mustbe such that magnetic saturation of the ferrite film 12 does not occurin any region thereof, prior to that of the region of the film betweenthe conductors and the plane of the meander line.

In FIG. 2 is shown the conducting film 25 including the tab pairs 26 and27. If desired, an opening 24 (not shown in FIG. 3 to simplify theillustration thereof) may be proprovided to assure spreading, or moreuniform distribution of the current in an energized current path. Moreparticularly, the film 25 is energized by supplying current thereto in acircuit including a pair of oppositely disposed tabs. Thus, there isshown by dotted lines a representative current path 26 for the circuitincluding tabs 26.

In FIG. 3, the current conducting path through the film 25 and definedby the tabs 26 is shown connected in an energizing circuit including aswitch 30 at one end and a switch 31 at the other end, the latter beingconnected to a ground potential terminal. Similarly, the current pathdefined by the pair of tabs 27 is shown connected in an energizingcircuit including a switch 32 at one end thereof and a switch 33providing connection to a ground potential terminal. Each of theswitches 30 and 32 is connected to a suitable energizing source,represented by a positive potential power supply terminal. Uponselective closure of each of the switch pairs 30, 31 and 32, 33, a pulseof energizing current is caused to flow through the respectivelyassociated conducting paths in the film 25 to create a coercive, orapplied, D.C. magnetizing field of a related orientation for fluxdriving the ferrite film 12 to a state of remanent magnetization of thatsame orientation. The orientations of the applied magnetizing fieldsgenerated by the current pulses conducted through the paths defined bythe tabs 26 and 27, and thus of the remanent magnetization of theferrite film 12, are schematically represented by the flux pathslabelled H and H associated with the corresponding pairs of tabs 26 and27 which define the latching current paths.

The principal direction of propagation of microwave energy through themeander line 14 is that defined by the long legs 14a of the line 14. Aspreviously described, the ferrite film 12 exhibits reciprocal latchingcharacteristics and thus the opposite directions of propagation ofmicrowaves through alternate ones of the long legs 14a of the meanderline 14 are immaterial as to the relative phase shift effected. Thefield H associated with the current path defined by tabs 26 thus isoriented at 0 with respect to, and thus parallel to, the primarydirection of propagation of microwave energy through the meander line14, as

defined by the major legs 14a. By contrast, the magnetizing field Hassociated with the current path defined by tabs 27 is oriented at 90with respect to, and thus perpendicular to, the direction of propagationand, particularly, is parallel to the short legs 14b of the meander line14. The alternate pulsing of these alternate current paths thus providesalternate directions of flux drive of the ferrite film to remanentstates in these same orientations.

In FIG. is shown a plot of the hysteresis curve of a magnetic medium,such as the ferrite film 12, in accordance with an applied magnetizationfield, such as generated by a latching current pulse conducted by eitherof the latching current paths as above defined. As is well known, thestrength of the applied magnetizing field H is a function of theamplitude of the magnetizing current. Further, the resultantmagnetization B of the medium, such as the ferrite film 12, is afunction of the amplitude of the applied magnetizing field H, andincreases with increasing values of H until magnetic saturation of themedium is reached. When the pulse terminates and thus upon reduction ofthe latching current to zero value, the value H of the magnetizing fieldsimilarly reduces to zero value. The magnetization of the medium thenreduces to the remanent magnetization value identified as the remanentlevel B in FIG. 5. Similarly, a latching current of opposite polarityand of sufficient amplitude, creates a magnetizing field -H which drivesthe ferrite medium to saturation in a negative direction; upontermination of the current, the medium returns to an opposite sense, orpolarity, remanent level B,..

As discussed previously, the ferrite phase shifter of the invention isreciprocal, and thus regardless of the direction, or sense of theremanent magnetization, i.e., +B or B,, which is established, thecontrol of the relative phase shift will be in accordance with thecorresponding component of magnetization oriented with the direction ofpropagation of the microwave through the meander line 14. Thus, bysupplying a sufiiciently high current pulse to a selected one of thelatching current conductor paths 26 and 27, magnetizing fields H ofsufficient intensity to drive the ferrite layer 12 to a latchedcondition in the corresponding orientations as previously described mayproduce either a maximum or a minimum amount of relative phase shift,respectively, in a microwave transmitted through the meander line 14.

The field interaction which accomplishes the relative phase shift isillustrated in the cross-sectional view of FIG. 4 To facilitateillustrating the relationship of the interacting fields, thecross-sectional view includes selected, or broken, sections across thewidth of the phase shifter 10, along the line 4-4 in FIG. 3. As abovenoted, the meander line 14 and the ground plane 18 define the microwavetransmission line for the system. The T.E.M. mode of transmission isrepresented in FIG. 4 with respect to three of the major legs 14a of themeander line microstrip 14. The RF. electric field vector is thus shownestablished between the legs 14a and the ground plane 18, traversing thedielectric layer 16, and the RF. magnetic field is represented by closedelliptical paths labelled H The cross section of the FIG. 4 furtherillustrates the remanent field in the ferrite 12 produced by pulsing ofthe current path 27, the remanent field similarly being shown as aclosed elliptical path labelled B Although not shown, it is readilyapparent that the remanent field B which is parallel to the major legs14a of the mean der line would be therefore perpendicular to themagnetic field H produced by the propagated microwave. Similarly, thefield B will be perpendicular to the field H in the region of the shortlegs 14b of the meander line and the field B, will be parallel to thatfield.

Selective pulsing of the conductor paths 26 and 27 therefore providesfor establishing a remanent field exactly parallel to, or exactlyperpendicular to the primary or principal direction of propagation ofthe microwave through the meander line 14. The flux drive capability ofthe phase shifter of the invention thus provides for rotating theorientation of the saturated magnetization of the ferrite film in aplane of rotation parallel to the plane of the microstrip line 1 4.

The phase shift of a phase shifter is measured as the total phase changebetween the input and the output as a function of the length of theconducting or transmission line therein. The differential phase shift,similarly, is a measure of the phase change per unit length oftransmission line. The maximum net differential phase shift thus is afunction of the difference between the total length of the major legs14a and that of the minor legs 14b.

Where purely digital operation is desired, it Will be apparent that thelatching conductor paths should be energized with current pulses whichexceed that required to establish the remanent magnetization condition.The amount of relative phase shift is also a function of the length ofthe ferrite in the direction of propagation, its physical configuration,and the length of the transmission line effected by the magnetizationfield produced in the ferrite. Thus, phase shifters of the type of theinvention may be constructed to have desired amounts of relative phaseshift for given microwave frequencies. A plurality of the phase shiftershaving appropriate characteristics therefore may be employed in a tandemarrangement and digitally controlled in various combinations to give awide range of relative phase shifts.

Alternatively, for analog type applications, the amplitude of thelatching currents may be controlled for providing intermediate steps, oramounts, or differential phase shift. As above noted, the amount ofdifferent phase shift is a function of the component of magnetization inthe direction of propagation. The component may be adjusted in amplitudeby controlling the amplitude of the magnetization of the ferrite layeraligned with the direction of propagation, through driving the latchedferrite layer through a minor loop of the hysteresis curve to a point orreduced amplitude remanent magnetization as indicated at B, in FIG. 5.Such control of magnetization through a minor loop requires energizationof a selected current path of a controlled amplitude current pulse ofopposite polarity to that which initially produced the remanentmagnetization B,., but of less ampli tude than that which would causesaturation of the film in the opposite polarity.

In accordance with a further embodiment of the in vention shown inplanar and cross-sectional views in FIGS. 6 and 7, respectively, theconducting film also serves as a ground plane for the transmission line.In FIGS. 6 and 7, to which reference is made concurrently in thefollowing description, portions of the phase shifter which aresubstantially identical to those of the preceding figures are identifiedby identical, but primed numerals. The phase shifter thus includes ameander line 14' deposited on the upper surface of a ferrite film 12',the latter having formed therein at an intermediate position aconducting film 25' which provides selectively energizable latchingcurrent conductor paths for latching the film 12' in desiredorientations with respect to the meander line 14'. If desired, aprotective layer 16' of dielectric, or insulating type material may beformed over the meander line 14'.

As best seen in FIG. 7, the ferrite film 12 includes a lower layer, orportion, 12a and an upper layer 12b between which is formed theconducting film 25, the layers 12a and 12b being integral in regionssurrounding the outer boundary or perimeter of the film 25'. For areason to be explained, however, the upper layer 12b of the film 12' iselongated relatively to the lower layer 12a and thus includes laterallyextending arms. The conducting film similarly includes lateral arms 25a'formed on the lower, exposed surface of the upper layer 12b of the film12'. The lateral arms of the film 25' are integral with the tabs 26'and, as will be shown, provide electrical connection thereto. Themeander line 14' also includes lateral extensions 14a extending over thearms of the ferrite layer 12b.

Coaxial connectors and 22' are provided for external connection to themicrostrip transmission line and include central conductors 21' and 23,respectively, connected to the extensions 14a of the transmission line14' and outer connectors connected to the lateral extensions of theconducting film 25. The film extensions are integral with and thuselectrically connected to the tab pairs 26' of the film 25'.

The phase shifter of FIGS. 6 and 7 is most conveniently constructed bydepositing the lower layer 12a of the film 12 in the same dimensions asthe upper layer 12b, as seen in FIG. 6, and in successive stepsdepositing the conducting film 25' including the lateral extensions 25aand the second layer 12b of the film 12. Suitable photoresist techniquesmay then be employed for removing portions of the lower layer 12a of thefilm 12 to expose the conducting film extensions 25a in the finalconfiguration as shown in FIG. 7. Following this construction, themeander line 14 including extensions 14a may be deposited and aprotective, insulating layer 16 then formed over the full extent of theupper layer 12b of the film 12'.

The provision of the lateral extensions of the upper layer 12b of thefilm 12' and of the associated conducting film extensions 25a, andmeander line extensions 14a provide both for convenience of makingexternal connections and for isolation of external connection terminalsfrom the region of the primary field interaction of the remanent D.C.magnetization of the film 12 and the RF. field associated with amicrowave propagated through the meander line 14'.

The operation of the structure of FIGS. 6 and 7 is substantiallyidentical to that of the foregoing figures and thus there are providedswitches 30' through 33' which function in a manner substantially asdescribed with respect to the switches 30 through 33 to flux drive theferrite film 12 to effect selected phase shift characteristics. Asubstantial distinction of the structure of FIGS. 6 and 7 from that ofthe foregoing figures, however, is that the upper layer 12b of theferrite film 12' now serves as a dielectric, spacing the meander line 14from the conducting film 25 wherein the latter now serves as the groundplane. The meander line 14', the upper layer 12b of the ferrite film12', and the conducting plane 25' now define the microwave transmissionline of the phase shifter. Thus, the use of a conducting film permitssimplification of the structure of the phase shifter and reduction incost by permitting elimination of a separate ground plane, whileproviding a more uniform remanent magnetization field distribution inthe ferrite throughout the interaction region with the RF. magneticfield of the propagated microwave.

In summary, the latching ferrite reciprocal phase shifter of theinvention is of compact size and simplified construction, and provideslatched or remanent magnetization fields having a distribution whichmaximizes the parallel, or alternatively, perpendicular relationshipthereof to the microwave transmission circuit. The phase shifter isadaptable for either digital or analog operation, and a pluralitythereof may be employed in a tandem arrangement and controlled tooperate in various combinations for providing a wide range of selectiveamounts of phase shift.

I claim as my invention:

1. A reciprocal latching phase shifter for microwave transmission in theT.E.M. mode comprising:

a ferrite film having lower and upper layers,

a microwave transmission line associated with said film and defining thedirection of microwave propagation with respect to said film,

a conducting film formed integrally with said ferrite film between saidlower and upper layers, and including means defining selectivelyenergizable current paths therethrough for applying magnetizing fieldsto said ferrite film in predetermined orientations with respect to thedirection of microwave propagation, and

said lower and upper ferrite layers being integrally formed in theportions of said ferrite film surrounding said conducting film to definecompleted magnetic circuits respectively flux driven by said selectivelyapplied magnetizing fields to establish corresponding remanent fields ofmagnetization of said ferrite film, the remanent fields being displacedin orientation through a plane of rotation parallel to the plane of themicrowave transmission line, and interacting with a microwave propagatedthrough said transmission line to effect corresponding, selectivecontrol of the relative phase shift of a microwave thus propagated.

2. A phase shifter as recited in claim 1 wherein:

said conducting film and said integrally formed portions of said ferritefilm layers structure said ferrite film to define double toroids, and

said path defining means of said conducting film are respectivelyassociated with said thus defined double toroids of said ferrite filmfor selectively flux driving said ferrite film to saturation toestablish remanent fields of magnetization of predetermined orientationsdefined by the selectively energized current paths and respectivelyassociated double toroids.

3. A phase shifter as recited in claim 1 wherein:

said conducting film and said layers of said ferrite film are integrallyformed in parallel relationship and of similar configuration, with saidconducting film having boundaries of smaller dimensions than saidferrite film, and

said path defining means of said conducting film comprises integralconnector tabs formed in pairs at opposed boundaries of said conductingfilm and extending to the perimeter of said ferrite film to permitexternal connection to said conducting film for selective energizationof the current paths defined thereby.

4. A phase shifter as recited in claim 3 wherein:

said layers of said ferrite film are integrally formed in the portionsthereof surrounding the boundaries of said conducting film andintermediate said connector tabs to define said completed magnethiccircuits.

5. A phase shifter as recited in claim 3 wherein:

said conducting film includes two pairs of said connector tabs relatedto each other to define substantially orthogonally related current pathsthrough said conducting film, and

one of said orthogonally related current paths is substantially parallelto the principal direction of propagation of said microwave through saidmicrowave transmission line.

6. A phase shifter as recited in claim 1 wherein said microwavetransmission line of said phase shifter includes:

a microstrip formed on the upper surface of said supper ferrite layer,and

means defining a ground plane in parallel, spaced, and

insulated relationship to said microstrip.

7. A phase shifter as recited in claim 6 wherein:

said means defining a ground plane comprises said conducting film, and

said upper layer of said ferrite film provides the parallel, insulated,spacing of said microstrip from said conducting ground plane.

8. A phase shifter as recited in claim 1 wherein:

said microwave transmission line comprises a meander line having aplurality of parallel main legs defining the principal direction ofpropagation of the microwave and a plurality of smaller legsperpendicular to 11 v 12 and joining said main legs in a series circuitcon- References Cited new, and UNITED STATES PATENTS the relative phaseshift of the microwave propagated through said meander line is afunction of the net 3,447,143 5/1969 Half et 333-31 difference of thetotal length of the main and smaller legs of the meanderline' 5 ELILIEBERMAN, Primary Examiner 9. A phase shifter as recited in claim 8wherein: P. L. GENSLER, Assistant Examiner the boundaries of saidconducting film are of larger dimensions than the boundaries of themeander line US. Cl. X.R.

portion of the microwave transmission line. 10 33324.1, 84

